1. Field of the Invention
The present invention relates to curable organopolysiloxane compositions. More specifically, the present invention relates to curable organopolysiloxane compositions which cure by the addition reaction of silicon-bonded lower alkenyl radicals with silicon-bonded hydrogen atoms and exhibit excellent adhesion to a variety of substrates.
2. Description of the Prior Art
Organopolysiloxane compositions curable by a platinum catalyzed addition reaction of an organohydrogensiloxane to an organopolysiloxane containing ethylenically unsaturated hydrocarbon radicals have heretofore been used in numerous fields of industry because they do not generate by-products during curing, because they can be cured by heating at relatively low temperatures for short periods of time, and because they have an excellent flame retardancy and the ability to function as electrical insulators.
However, because addition-curable organopolysiloxane compositions do not adhere well to substrates with which they are in contact during curing, the surface of the substrate must be preliminarily treated with a primer. This is disadvantageous from the standpoints of productivity, labor and cost. As a consequence, numerous techniques have been proposed for imparting adhesion by, among other means, the blending of particular types of silanes and polysiloxanes into such compositions. Among these, there have been more than a few proposals to the effect that an unsaturated group-containing organosilicon compound be added as an adhesion promoter. Organosilicon compounds proposed for this purpose include acryloxyalkyl group-containing silanes or siloxanes as taught in Japanese Patent Publication 51-28309 (28,309/76), unsaturated group-containing alkoxysilanes disclosed in Japanese Patent Publication 56-9183 (9,183/81), partial hydrolyzates of the aforementioned unsaturated group-containing alkoxysilane as taught in Japanese Laid Open Patent Application (Kokai) Number 54-135844 (135,844/79), partial hydrolysis condensates of mixtures of a vinyltrichlorosilane and a vinyltrialkoxysilane as taught in Japanese Patent Publication 47-36255 (36,255/72), and organopolysiloxanes having acryloxy or methacryloxy groups at the molecular terminals as disclosed in Japanese Patent Publication 55-39258 (39,258/80).
While the adhesion promoters disclosed in the aforementioned prior art provide excellent adhesion to metals, the curable compositions suffer from the problem that the adhesion to plastics in particular is unsatisfactory.
Accordingly, the present inventors examined various methods in order to overcome the problem in said prior art, and the present invention was developed as a result.
An objective of the present invention is to provide a curable organopolysiloxane composition which will tightly bond to substrates such as metals, glass, ceramics, stone, concrete, wood, paper, fibers, rubber and leather, and which in particular will also tightly bond to substrates to which good adhesion has not previously been possible. Substrates of this latter type include plastics such as polybutylene terephthalate, polycarbonates, polyolefins, polyphenylene oxide, polyamides, and polyphenylene sulfide.